1. Field of the Invention
The present invention relates generally to a CDMA demodulation circuit, a CDMA mobile communication demodulation method used therefor, and storage medium recording program thereof. More particularly, the invention relates to a demodulation method in CDMA (Code Division Multiple Access) mobile communication.
2. Description of the Related Art
Conventionally, in a reception process of the CDMA mobile communication, a received signal is segregated into a plurality of multiple path components having different propagation periods by despreading using spreading code replica synchronized with spreading code of the received signal. In this case, a desired wave has to be despread by spreading code replica synchronized with reception timing of the signal and has to detect reception timings of respective passes.
In this reception process, a timing of the spreading code replica in a symbol of information 1 is shifted per one chip for despreading over one symbol period to generate a power delay profile. From generated power delay profile, passes are selected in order from those having large reception power per number of rake fingers to establish a path for rake synthesis.
Since positions (delay periods) of paths to be rake synthesized are frequently fluctuated associating with movement of the mobile station, the power delay profile is regularly updated per a given interval in the receiver for also effecting updating of the rake synthesizing paths. This is to retrieve paths for rake synthesis and thus is referred to as path search.
In the demodulation circuit to be used in the reception process of the foregoing CDMA mobile communication, diversity effect is attained by the path search and rake synthesis. In a mobile communication environment, the received radio wave often becomes multiple path environment to be influenced by level fluctuation and fluctuation of arrival period to reception point. If error is caused in finger despreading timing under such sever path fluctuation, reception characteristics can be deteriorated.
Therefore, in the foregoing demodulation circuit, it is desired to search stable path among arriving paths and to effect an appropriate finger despreading timing detection process adapted to fluctuation of path arrival period.